LOWELL — Sixteen days before the election, the Republican and Democratic candidates for US Senate warned voters of the race’s high stakes, as each portrayed the opposition as a standard-bearer for partisans.

As Democrats charged that a vote for incumbent US Senator Scott Brown is a vote for a Republican majority in the US Senate, Brown told supporters that he represents “good moderates” trying to bring the country together. He rallied a crowd of about 120 supporters in an auditorium at the University of Massachusetts Lowell, where he was joined by his wife, Gail Huff, his daughter, Arianna Brown, and New Hampshire US Senator Kelly Ayotte.

Ayotte targeted Democrat Elizabeth Warren, saying the country doesn’t need someone who will consistently vote with the party.

“That’s who she is. She’s an ideologue,” said Ayotte. “Scott is the most bipartisan senator in Washington.”

Meanwhile, Warren held her own rally in Northampton, packing a gymnasium in the Smith Vocational and Agricultural High School, where she said she would overturn the Defense of Marriage Act and targeted Brown’s record on women’s rights.

“Scott Brown had one chance to vote for equal pay for equal work,’’ Warren told the crowd. “He had one chance to vote for insurance coverage for birth control and he had one chance to vote for a prochoice woman to the United States Supreme Court. He voted no, he voted no, and he voted no. Let me make this clear: I want to go to Washington to stand up for women.”

The concerns of gay groups and women were at the top of Democrats’ agenda in recent days, as they sought to nationalize the Senate race, warning voters in new ads and mailers that a Brown reelection could tip the balance in the Senate to “extreme Republicans.” The Massachusetts Democratic Party on Friday launched a website that ties Brown to “dangerous Republicans who could take power” and to a more “radicalized America.”

Warren launched a new ad Friday that warned that Republican control of the Senate could result in deep cuts to education and Medicare, new tax breaks for millionaires, and a new Supreme Court justice who could overturn the law legalizing abortion.

The Brown campaign on Friday released a new ad highlighting his bipartisan appeal, noting he was ranked the second most bipartisan senator in 2011.

“I was the tiebreaking vote to pass Wall Street reform, supported the right of gay servicemen and women to serve openly in the military, and defended Planned Parenthood and women’s health services from cuts,” he says in the statewide TV ad.

At his event, Brown was bolstered by the former mayor of Lowell, Rita Mercier, who pointed to Brown’s wife and daughters as evidence of his support for women, calling them “three adorable good woman that are strong and vibrant and independent. You don’t get that way unless you have a strong man that allowed you to blossom.”

“Don’t believe the lies,” Mercier said. “Last time I checked, I’m a woman, and I support him.”

Brown cited his endorsements by Mercier and three other former mayors of the four largest cities in Massachusetts — Raymond L. Flynn of Boston, Charles V. Ryan of Springfield, and Konnie Lukes of Worcester. All are Democrats who Brown said were heartened by his efforts to “push back against the extremes on the right and the left.”

“We do not need someone down there who’s going to be in lockstep, be part of the problem, be part of that extreme group on the left and the right,” Brown said. “Because right now, that middle is dwindling. People like me are a threat to what’s going on down in Washington.”

The campaigns also followed similar agendas Sunday, a day after hosting dueling appearances with decorated war heroes as they appealed to veterans.

Before their rallies with supporters, Warren and Brown started their Sundays attending services at churches with predominantly black congregations.

Neither candidate publicized the church services and each campaign said the candidate occasionally visits churches without promoting the appearances.

Warren attended services at four African-American churches in Springfield.

Brown appeared with his wife and daughter and former Mayor Flynn at Grace Church of All Nations in Dorchester.

Warren spoke there several weeks earlier and soon picked up the endorsement of Boston’s prominent political black ministers.

Brown’s Sunday appearance had been scheduled for months, said Kevin Peterson, executive director of the New Democracy Coalition. He spoke for about 10 minutes, Peterson said, passionately recalling his difficult upbringing in an abusive household. “So he knows directly about redemption. He knows about finding trust in others and trust in God,” Peterson recounted.

The Rev. Jeffrey Brown, a member of the group of black clergy that endorsed Warren, said he couldn’t remember a time that both parties spent this much time and money in communities of color. He said that in Grove Hall, Brown has an office and two billboards showing him with President Obama.

“I think it’s healthy to see both major parties see the value of the vote of communities of color in this election cycle,” he said. “It says a lot about the importance of getting every vote this time around.”